The present invention relates to the technical field of data processing and serial communication, for example, to effective technology to be applied to a microcomputer having a serial communication interface. Since microcomputers can constitute desired sequential logic in programming by software, processing of high degree can be performed in a wide application field and some microcomputers have a serial input/output circuit such as data processing terminal or modem to enable data transmission/reception with the outside in a bit serial manner.
Data transmission control procedures for transmission/reception of data in bit serial manner include various sorts of procedures such as the well-known high level data link control (HDLC) procedure and the binary synchronous communication (BSC or BI-SYNC) system, and further a start-stop synchronous procedure. However, a serial input/output circuit installed in a microcomputer or the like in the prior art merely supports one among the above-mentioned data transmission control procedures, for example, i8044 described in "Distributed Control Modules Data Book" published by Intel Company in 1984 only supports the HDLC procedure. The above-mentioned procedures are described on pp. 337, 338, 625 and 626 in "MICROCOMPUTER HANDBOOK" published by Ohm Company in 1985. As low cost of logic LSIs such as a microcomputer advances, these devices are apt to be multifunctional. Particularly paying attention to the serial interface function, since the above-mentioned three sorts of data transmission control procedures have a wide application field corresponding to respective advantages, the present inventor has found that these devices must be able to support a plurality of data transmission control procedures also to a serial input/output circuit contained in a data processing LSI such as a microcomputer so that multifunctional serial communication as required can be attained.
Further in this case, since the LSI chip cannot be made large without limitation from the viewpoint to manufacturing and economy, when a plurality of data transmission control procedures are supported, such condition must be also considered that the logical scale can be minimized.